OpenVZ is container-based virtualization for Linux. OpenVZ creates multiple secure, isolated containers (otherwise known as VEs or VPSs) on a single physical server enabling better server utilization and ensuring that applications do not conflict. Each container performs and executes exactly like a stand-alone server; a container can be rebooted independently and have root access, users, IP addresses, memory, processes, files, applications, system libraries and configuration files. For more information about the technology and how it differs from the others like Xen, VMware etc., see introduction to virtualization, doc/openvz-intro.pdf (73 KB) or Wikipedia's OpenVZ (source: openvz).
In 2.6.29, openvz was included in the Debian linux source package (no need for extra linux-patch-openvz package)
The Debian 6.0 release notes include a warning that Debian 7.0 (wheezy) will no longer include a kernel which has been patched with the OpenVZ extensions. One of the following options must be used in order to use OpenVZ on Debian 7.0 (wheezy):
The wheezy-specific OpenVZ kernels from http://download.openvz.org/debian/
A limited subset of the OpenVZ functionality is available with newer vzctl versions on sufficiently-recent mainline kernels http://wiki.openvz.org/Vzctl_for_upstream_kernel (i.e. relying on the same kernel features which LXC uses).
- The Red Hat Enterprise Linux 7 + OpenVZ kernels from openvz.org (when available), or possibly the currently-available RHEL6+OpenVZ kernels (TODO needs testing).
Alternatively, the LXC subsystem could be used (although some OpenVZ features are absent from LXC in Wheezy).
If you are the guest
Running Debian inside an OpenVZ container, as a guest, imposes some limitations that you must take into account.
- You are sharing the host's kernel. The kernel is probably very old by current standards (e.g. 2.6.26 or 2.6.32), and this will impose constraints on what software you can run.
- You can't use swap space.
- You are sharing the host's clock, and you can't set it from the guest. The host has to run NTP (or some other means of time synchronization). If your guest's clock is drifting, you'll have to contact your host provider to get it fixed.
Upgrading an OpenVZ container on the 2.6.* kernel should work fine up to Wheezy, but you must not upgrade to Jessie unless you take steps to prevent systemd from being used as the new init system.